[SigmundA]

The OSX Quartz graphic layer (also used in iOS) uses PDF internally as graphic object model.

It is no surprise iOS handles rendering PDF's so quickly and so well and without the need for an third party app, it always has from the release of the first iPhone. This is also why print to PDF is built in on OSX.

[gcr]

I thought it was postscript internally?

[dmd]

NeXT and NeWS were Display Postscript. OS X / Quartz is PDF.

[Someone]

It is more accurate to say that both Quartz and PDF (and Postscript) use the same primitives (cubic Beziers, color models, graphic state, etc)

PDF the file format adds many, many things to that (forms, encryption, DRM, notes, a JavaScript engine, reflow information, etc)